1. Field of the Invention
The present invention relates to a magnetoresistance effect film that uses the magnetoresistance effect to record and read information or to detect weak magnetic fields and to a method of forming the magnetoresistance effect film.
2. Description of the Prior Art
In recent years the magnetoresistance effect is being used to increase the sensitivity of magnetic sensors and to develop high performance magnetic heads for magnetic recording. These magnetic sensors and magnetic heads both read changes in resistance of the portion comprised of magnetic material produced by the application of the magnetic field to that portion, so research is focused on obtaining materials that exhibit a large change in magnetoresistance in response to a change in an external magnetic field.
Film of permalloy etc. exhibiting an anisotropic magnetoresistance effect has been used as a magnetoresistance effect material. However, the ratio of change in magnetoresistance exhibited by a material such as permalloy is only around two or three percent [IEEE Transactions on Magnetics, Vol. MAG-11, No. 4, p. 1018 (1975)], meaning it does not provide the type of performance that will be required by the high level information society of the future. Here, the change in magnetoresistance is defined as the amount of change in resistance produced by the application of a magnetic field that is the differential between the maximum resistance Rmax and the minimum resistance Rmin, and as shown by
xcex94R/R=100(%)xc3x97(Rmaxxe2x88x92Rmin)/Rmin,
the ratio of change in magnetoresistance is defined as a ratio between the amount of change and Rmin.
There is a new magnetoresistance effect material comprising a laminated artificial lattice film formed by alternating magnetic and nonmagnetic layers. This film exhibits a giant magnetoresistance effect that is dependent on the magnetic orientation of the magnetic layers coupled in an antiparallel magnetic fashion by the nonmagnetic layers. An artificial lattice film of Fe/Cr is a recent example of such research [Physical Review Letters, Vol. 61, No. 21, p. 2472 (1988)]. This type of artificial lattice film exhibits a magnetoresistance effect that is much larger than that exhibited by a conventional material such as permalloy, and in the case of an artificial lattice film of Co/Cu, a 65% magnetoresistance effect has been observed at room temperature [Applied Physics Letters, Vol. 58, No. 23, p. 2710 (1991)].
Further research has led to the proposal of the so-called spin-valve film having a sandwich structure of ferromagnetic metal layer/nonmagnetic insulating layer/ferromagnetic metal layer. This spin-valve film reads the change in magnetoresistance arising when the direction of the magnetization of one ferromagnetic layer against that of the other ferromagnetic layer changes by the applied magnetic field. As a result of recent intensive studies, a magnetoresistance effect at room temperature of as large as 10 to 20% has been reported [Physical Review Letters, Vol. 74, No. 16, p. 3273 (1995), and Journal of the magnetic society of Japan, Vol. 19, No. 2, p. 369 (1995)].
With respect to obtaining a large magnetoresistance effect with a small magnetic field, intensive studies are being conducted into granular magnetic films, which are films comprised of ferromagnetic particles dispersed in a nonmagnetic metal, semiconductor or insulator film matrix. While in the absence of a magnetic field such granular films exhibit high resistance, with there being no order to the direction of the magnetization of the magnetic particles, the application of a magnetic field produces a uniform alignment of magnetization that reduces the resistance, giving rise to the magnetoresistance effect. When the films were first developed, this effect was only obtained at low temperatures [Physical Review Letters, Vol. 68, No. 25, pp. 3745 and 3749 (1992)]. In subsequent studies, however, a magnetoresistance effect of several percent has been achieved at room temperature [Japanese Unexamined Patent Publication No. Hei 8-264858], and a magnetoresistance effect of 18% with a combination of ferromagnetic metal and nonmagnetic metal [Japanese Unexamined Patent Publication No. Hei 8-67966].
As an example of a new material that exhibits an even larger magnetoresistance effect, there is a report of a magnetoresistance effect of around 500% being achieved, at a low temperature, with UNiGa [Journal of Magnetism and Magnetic Materials, Vol. 104-107, p. 19 (1992)]. However, the effect was only observed at low temperatures.
Another recent research trend that can be mentioned relates to the giant magnetoresistance effect exhibited by perovskite oxides (Japanese Unexamined Patent Publication Nos. Hei 8-133894, 9-249497 and 9-263495, and U.S. Pat. No. 5,665,664). However, while such perovskite oxides exhibit several magnitudes of change in magnetoresistance at low temperatures, at room temperature the performance drops off dramatically, to a matter of several percent [Nature, Vol. 395, No. 6703, p. 677 (1998)], posing problems in terms of practical application.
The spread of medical, educational and commercial connection services using advanced communication systems and/or the Internet is creating a need for even larger-capacity storage technologies. To answer this need, it is necessary to develop magnetoresistance effect devices having an extremely high level of sensitivity.
The object of this invention is to provide a film that exhibits a colossal magnetoresistance effect of 73000% at room temperature (20xc2x0 C.) and 4000000% at xe2x88x9220xc2x0 C. and a method of forming the film.
To achieve the above object, the present invention provides a magnetoresistance effect film comprising a substrate, a plurality of ferromagnetic particles disposed on the substrate, a nonmagnetic film deposited on the substrate and covering the plurality of ferromagnetic particles, and a pair of electrodes provided each at a predetermined position on the nonmagnetic film, in which resistance across the pair of electrodes is changed by application of a magnetic field and provides a method of manufacturing a magnetoresistance effect film, comprising the steps of vapor-depositing ferromagnetic particle starting material on a substrate at a temperature not exceeding 300xc2x0 C., the starting material being vapor-deposited in an amount enough to cover a substrate surface to a thickness ranging from 0.5 to 15 nm, and, after formation of ferromagnetic particles on the substrate, vapor-depositing at a temperature not exceeding room temperature a nonmagnetic film over the ferromagnetic particles, the nonmagnetic film having a thickness ranging from 1 to 100 nm, and providing a pair of electrodes each at a predetermined position on the nonmagnetic film.
When an electric current or voltage is supplied to the film in the applied magnetic field, the change caused by electrons flowing in the nonmagnetic layer being scattered by the plurality of ferromagnetic particles gives rise to a giant magnetoresistance effect. This giant magnetoresistance effect is read by the pair of electrodes maintained a predetermined distance apart on the non-magnetic film, setting up a current flow across the electrodes via the nonmagnetic film, the interface between the ferromagnetic particles and the substrate and the interface between the nonmagnetic film and the substrate that undergoes a major resistance change as a result of the giant magnetoresistance effect produced by the mutual magnetic interaction between the ferromagnetic particles covered by the nonmagnetic film and the electrons flowing across the electrodes.
When the ferromagnetic particles and nonmagnetic film are constituted by a MnSb-Sb combination, the result is a giant magnetoresistance effect of some 300000% at 0xc2x0 C., and 4000000% at xe2x88x9220xc2x0 C.